The major components of the epididymal secretions of the mouse is a glycoprotein, gp70 (epi), which is antigenically and structurally related to, but distinct from, the envelope glycoprotein of murine leukemia virus, gp70 (MuLV). This molecule represent from 2 to 10% of the total protein found in epididymal secretions, is present in all mouse strains tested regardless of viral flora, and is not associated with viral particles. First, we will determine the relationship between gp70 (epi) and other classes of gp70. Gp70 (epi) will be purified, then used to prepare monospecific antibody. Next, we will determine the antigenic relationships among gp70 (epi), gp70s from various oncornaviruses, and molecules present in tissue from several species, including man. These assays will show the amount of gp70 (epi) in these materials as well as the extent of serologic crossreaction. Further, we will study the immunologic consequences of an immune response against gp70 (epi) in unmanipulated mice and in mice immunized with purified gp70 (epi). These studies will include the development of "autoimmune" disorders such as glomerulonephritis, orchitis, epididymitis. In addition, the reproductive capacity of mice immunized with gp70 (epi) will be examined by comparing sex ratio and litter size with those of control mice. Finally, the high concentration of gp70 (epi) in epididymal secretions encourages us to search for a function of this molecule in the biology of mouse sperm. We will determine whether gp70 (epi) is involved in capacitation or decapacitation of epididymal sperm, or whether gp70 is an epididymal enzyme or an inhibitor of such an enzyme.